It sounds too good to be true -- and that's because it probably is. As reported recently, scientists are claiming that simply sitting on the sofa and watching a movie can burn as many calories as a 30-minute walk.

Researchers at the University of Westminster found that horror films are the most effective calorie burners.

Watching a scary movie for 90 minutes causes the average viewer to burn 113 calories. It's been the couch potato's mantra for years -- and now, there's proof that doing nothing is actually good for you.

I'm not convinced. For a start, 113 calories isn't that impressive. Then there's the experiment itself.

Participants were wired up to monitors and made to watch a selection of horror films. That's enough to make anyone's heart race -- and where was the obscenely large bowl of microwave popcorn? In real life, scary movies do the diet plan no favours.

So what do the scientists have to say for themselves? "As the pulse quickens and blood pumps around the body faster, the body experiences a surge in adrenaline," explains metabolism specialist Dr Richard Mackenzie.

"It is this release of fast--acting adrenaline, produced during short bursts of intense stress -- or in this case, fear -- which is known to lower the appetite, increase the basal metabolic rate [BMR, the energy we expend while resting] and burn a higher level of calories."

Researchers found that the infamous "Here's Johnny" scene in the 1980 thriller The Shining made participants' hearts race fastest, burning 184 calories, while other fat-busters included the 1975 shark epic Jaws (161 calories), 1973's The Exorcist (158 calories) and the 1979 sci--fi film Alien (152 calories).

But surprise, surprise, feeling frightened is not a sustainable weight-loss strategy.

"You will probably compensate for it a couple of hours later by eating a big chocolate bar or heading to the pub," explains nutritionist Melanie Brown.

"It's also not healthy -- all that adrenaline goes into your muscles and it causes all sorts of problems with your blood-sugar levels. "

So, if scary movies don't help us fight the flab, in what other ways can exercise-phobes burn calories while doing, well, absolutely nothing?

Around 60pc of our daily calories are used up by the bodily processes involved in simply staying alive: sleeping, breathing and moving our limbs.

The average person burns 61 calories an hour while lying down, 68 when sitting up and a 88 while reading a book or newspaper.

If you're feeling more energetic, knitting is a great calorie--buster, burning 102 an hour. Wrapping presents, and playing cards or board games for 60 minutes, uses up more than 100 calories.

Typing and shuffling files have the same effect, while texting can burn up to 132 calories if done continually for an hour. Fidgeting can account for 350 calories a day, while chatting on the phone for 10 minutes burns 22 calories.

A few years ago, Women's Health magazine compiled a list of even more unlikely ways to burn 100 calories.

Claire Williamson, a nutrition scientist from the British Nutrition Foundation, warns that none of this should replace exercise.

"Sedentary behaviour is actually a risk factor in itself for ill health and obesity," she says. "The amount of time spent sitting has been found to have a negative impact on metabolic risk factors such as waist circumference and cholesterol level."

Earlier this year, scientists found that limiting the time we spend sitting to three hours a day could increase our life expectancy by two years.

And doing activities standing up expends 50 more calories than doing the same thing sitting down.

So slip in a scary DVD, pick up those knitting needles and try standing in front of the television instead.